This invention relates generally to metering devices for the precision feeding of a liquid medium, even in relatively small or minute quantities. Specifically, the invention relates to the construction of the evacuation valve for such metering devices.
Petroleum-based and synthetic lubricants, such as oil, are among the many liquids that are at times metered to machinery. In a given instance, the feeding of too little oil may place a machine at risk for excessive wear, damage or even catastrophic failure. However, too much oil may contaminate the product being manufactured and/or contribute to pollution and waste. Thus, accuracy in the metering of lubricants can be very important.
One such metering device is commercially known as the PurgeX® injector pump. The present invention comprises an improvement in such metering devices, including those described and claimed in U.S. Pat. Nos. 4,784,578, 4,784,584 and 7,118,352, each incorporated herein by reference.
These metering devices include an evacuation valve. The evacuation valve typically consists of a machined seal holder, or seal carrier, and a seal adhered or molded within the confines of an open chamber of the seal carrier. A portion of the seal protrudes from the seal holder to provide a critical sealing surface. In the past, one embodiment of the seal has been cut from sheet stock material and then affixed to the seal holder with adhesive. This construction has many drawbacks.
The primary drawback has been the inconsistency of the surface finish on the sheet material. Sheet material is likely to come from different suppliers and be handled in different manners during transport. If the surface finish is too rough, a poor seal will be provided by the evacuation valve. Furthermore, during the cutting process, great care must be taken to insure that the resulting cut seal is flat and that the seal edges are unobstructed and substantially perpendicular to the seal surface. If the edges are tapered, concave or convex, the seal is likely to function poorly. In other instances, the resulting cut seal has a skewed or trapezoidal shape when viewed from the front. Such shaped seals again perform poorly. The cutting process often generates debris that must be removed before the gluing process. In addition, the seal must be further cleaned to remove any oils or other contaminates, again prior to the gluing process. The selected adhesive used to join the seal with the seal holder must be compatible with the lubricant or fluid that will be dispensed through the metering device. Selecting an incompatible adhesive will ultimately lead to valve failure.
During the gluing process, great care must be taken again to insure that none of the glue is dispensed upon or makes contact with the seal surface. Further, it is important to insure that the seal is properly positioned and centered within the seal holder, or carrier. As can be appreciated, the entire process is quite labor intensive and requires multiple inspections of the parts prior to and during assembly.
Another design has an open cavity formed in the seal carrier. The seal carrier is placed in a mold having another open portion adjacent to the cavity. Liquefied seal material, typically an elastomeric material is then injected through the carrier and into the mold thereby forming the seal within the space defined by the open cavity and the open mold portion. The seal includes a smooth, flat sealing surface located above the seal carrier formed by the open space. When the mold halves are separated, a finished evacuation valve 20 is removed from the mold.
This design also has drawbacks. For example, during the molding removal process the rubber seal material can pull out of the holder resulting in a seal that is not flat. A molded seal having a concave or convex seal surface can lead to a potentially leaking evacuation valve. Due to the formation of a hex broach within the mold cavity of the seal carrier to prevent rotation, once the molded seal became partially dislodged from the carrier, it cannot simply be pushed back in. During the molding process, there is a potential for excess seal material to form flash on the top surface of the carrier. If not removed, the flash material is likely to come loose during operation of the evacuation valve and thus prevent proper sealing. To prevent this situation, any flash material must be removed from the evacuation valve after molding and before installation in the metering device. Again, the entire process is quite labor intensive and requires multiple inspections of the parts prior to and during assembly.
The present invention overcomes these shortcomings by providing an evacuation valve that utilizes an O-ring. As described herein, the resulting valve is more economical to produce, has a superior sealing surface, and will provide a longer service life.